1. Field of the Invention
The present invention relates to a display apparatus and a control method thereof.
2. Description of the Related Art
One function of a display apparatus is the function of displaying a plurality of images together. The function of displaying the plurality of images is, for example, a function of displaying a plurality of images in a display mode such as PinP (picture-in-picture) display or PoutP (picture-out-picture) display. In the PinP display, a single image is displayed, and at least one image is displayed on the single image. In the PoutP display, a plurality of images are displayed so as not to overlap each other.
Recently, market demands for improvement of display characteristics of display apparatuses have been increasing. As a technology for improving the display characteristics of liquid crystal display apparatuses, there is a technology of controlling the light emission brightness of a backlight on the basis of the characteristic value of an image (e.g., average brightness level (APL)) (Japanese Patent Application Laid-open No. 2007-140483).
Additionally, as the technology for improving display characteristics of liquid crystal display apparatuses, there is a technology of performing local dimming control of a backlight (Japanese Patent Application Laid-open No. 2002-99250). In local dimming control, the light emission brightness of the backlight is controlled per divided region obtained by dividing a screen. With reference to FIG. 13, the local dimming control will be described. As light sources of the backlight, light emitting diodes (LEDs) having better light emission efficiency than cold-cathode fluorescent tubes have started to become mainstream. A backlight in FIG. 13 has LEDs as the light sources. In the example of FIG. 13, the backlight is configured from 60 LED control regions corresponding to 60 divided regions of 10 in the horizontal direction×6 in the vertical direction. Light sources (four LEDs in the example of FIG. 13) are provided in each divided region (each LED control region). The light sources in each divided region can be individually controlled. The light emission brightness of the divided region (light emission brightness of the backlight) where a dark image is displayed is made lower than the light emission brightness of the divided region where a bright image is displayed, thereby enabling an improvement of the contrast of a displayed image (image displayed on a screen).
Generally, the number of the divided regions is smaller than the number of pixels of a display panel (liquid crystal panel). That is, a single divided region is a region including a plurality of pixels. The number of pixels of the liquid crystal panel, which are used in the liquid crystal display apparatus, tends to increase year after year, and about 2 million pixels (e.g., 1920 pixels in the horizontal direction×1080 pixels in the vertical direction) has become mainstream.
However, when the aforementioned local dimming control is performed at the time of display of a moving image together with a still image, the visibility of the still image is sometimes lowered (image quality of the still image deteriorates). For example, at the time of displaying of the still image and the moving image in a PinP mode, when the aforementioned local dimming control is performed, the light emission brightness of the divided regions where at least a part of the moving image is displayed is changed due to a brightness change of the moving image, as shown in FIG. 14. As a result, flickering in brightness, halation, or the like, is generated in a peripheral region 1601 of the moving image in the still image. Also, in a case where the display position of the still image is changed when the local dimming control is performed and a plurality of still images are displayed together, the visibility of the still image is reduced. For example, in a case where two still images (a still image a, and a still image b) are displayed in a PoutP mode as shown in FIG. 15A, when the display position of the still image b is changed as shown in FIG. 15B, flickering in brightness, halation, or the like is generated in a peripheral region 1501 before and after the change of the display position of the still image b.